This invention relates to an ink jet recording head wherein a piezoelectric element is formed via a diaphragm in a part of each of pressure generating chambers communicating with nozzle orifices for jetting ink drops and ink drops are jetted by displacement of the piezoelectric element, and an ink jet recording apparatus comprising the ink jet recording head.
The following two types of ink jet recording heads, each wherein a part of a pressure generating chamber communicating with a nozzle orifice for jetting an ink drop is formed of a diaphragm and the diaphragm is deformed by a piezoelectric element for pressurizing ink in the pressure generating chamber for jetting an ink drop through the nozzle orifice, are commercially practical. One uses a piezoelectric actuator in a vertical vibration mode in which the piezoelectric element is expanded and contracted axially and the other uses a piezoelectric actuator in a deflection-vibration mode.
With the former, the volume of the pressure generating chamber can be changed by abutting an end face of the piezoelectric element against the diaphragm and a head appropriate for high-density printing can be manufactured, but a difficult step of dividing the piezoelectric element like comb teeth matching the arrangement pitch of the nozzle orifices and work of positioning and fixing the piezoelectric element divisions in the pressure generating chambers are required and the manufacturing process is complicated.
In contrast, with the latter, the piezoelectric element can be created and attached to the diaphragm by executing a comparatively simple process of putting a green sheet of a piezoelectric material matching the form of the pressure generating chamber and baking it, but a reasonable area is required because deflection vibration is used; high-density arrangement is difficult to make.
On the other hand, to solve the problem of the latter recording head, Japanese Patent Publication No. 5-286131A proposes an art wherein an uniform piezoelectric material layer is formed over the entire surface of a diaphragm according to a film formation technique and is divided to a form corresponding to a pressure generating chamber according to a lithography technique for forming a piezoelectric element separately for each pressure generating chamber.
This eliminates the need for work of putting the piezoelectric element on the diaphragm and the piezoelectric element can be created by the lithography method, an accurate and simple technique. In addition, the piezoelectric element can be thinned and high-speed drive is enabled. In this case, with the piezoelectric material layer provided on the whole surface of the diaphragm, at least only upper electrodes are provided in a one-to-one correspondence with the pressure generating chambers, whereby the piezoelectric actuator corresponding to each pressure generating chamber can be driven.
In such an ink jet recording head, generally a reservoir which becomes an ink chamber common to pressure generating chambers is formed by depositing a plurality of substrates on each other, and ink is supplied from the reservoir to the pressure generating chambers. To hold the internal pressure of the reservoir constant, the reservoir is provided with a compliance section for absorbing pressure change when a piezoelectric element is driven.
However, a large number of substrates used to form the reservoir are required; particularly a large number of substrates deposited to form the compliance section are required, increasing material and assembly costs.
The ink jet recording head as described above is intended to have a large number of nozzles and it is necessary to form the reservoir in size capable of sufficiently supplying ink to the pressure generating chambers accordingly; the strength of the substrates forming the reservoir is degraded inevitably. Thus, if heat is applied to the substrates at an installation step, the substrates are warped due to thermal expansion and a crack occurs.
To use silicon for the substrate for defining each pressure generating chamber, it is difficult to bond at a high temperature because of the difference from other substrates in thermal expansion coefficient and the number of assembly steps is increased.